You'll have the best luck finding patterns like this on sites that sell sewing patterns for modest clothing or vintage patterns. Try Googling these phrases:

sew pattern modest clothing
sew pattern girl vintage bloomer

Here are a few patterns I found:
#FP020. Bloomers Pattern, 3 variations, girls sizes thru women's XL
Girl's pantaloons with ruffles; you can probably shorten these

Another option is vintage patterns, for example:
Toddler dress and bloomers pattern, 1997
The shortie PJ bottoms in view D

***I've purchased vintage patterns from Lanetz Living and have had very good service and prices.

HTH,
CMC

Check out the patterns for Raggedy Ann costumes. I made myself a costume and it had the bloomer pattern. Should have it for kids too. There should be prairie girl costumes and they should have bloomer patterns too.
Kathy G in MI

Here is a link that might be useful: Raggedy Ann costume pattern

Hey Blessed,

I am a quilter who recently got into sewing for the grandbaby. Simpliicty 4505 has a great pattern for undergarments. We used it in class to make pantaloons it was great. My grand is a 3T.

Hope that helps.

Nanci

I think Nanci means McCalls 4505. M4505 is very cute slips, camisoles, panties and bloomers. Wow, Nanci! I don't even have grandkids yet, but I think I need this for my collection.

Size groupings are 3-4-5-6 and 6-7-8.

McCalls 4505 CHILDREN'S/GIRLS' SLIPS, CAMISOLES, PETTICOAT, PANTIES AND BLOOMERS

CMC

Here is a link that might be useful: McCalls 4505

Thanks!!! I just have to decide which to try first. Thanks for sharing your knowledge and experience.
Julie